Electrical generators are used in a wide variety of applications. Typically, an electrical generator operates in a stand-by mode wherein the electrical power provided by a utility is monitored such that if the commercial electrical power from the utility fails or is otherwise interrupted for a certain period of time, the engine of the electrical generator is started, either automatically or manually by a customer, causing the generator to supply emergency or backup electrical power. More particularly, the engine drives an alternator to provide electrical current to power selected electrical loads that are connected to the electrical generator, which is typically through a dedicated electrical panel, i.e., transfer panel.
When the electrical power generated by the alternator reaches a predetermined voltage and frequency desired by the customer, a transfer switch transfers the load imposed by the customer from the commercial power lines to the electrical generator. The electrical generator then supplies electrical power to selected loads, which are typically deemed to be critical loads, such as HVAC equipment, refrigerator(s), lighting, and, if applicable, medical equipment.
Larger electrical generators, which are typically used to provide backup or standby electrical power to larger dwellings, commercial and retail spaces, offices, and hospitals and medical facilities, are generally started by means of a battery-powered starter motor. Typically, the starter battery is kept charged with a charging current developed by the generator as the generator operates. Over time however the maximum charge of the battery will decline until ultimately the battery lacks the charge to energize the starter motor and the electrical generator will be unable to supply backup electrical power.
In a conventional arrangement, the battery is charged simply as a function of the electrical output of the alternator and therefore when the alternator is operating at or near full capacity, a maximum charging current is supplied to the battery regardless of the current charge of the battery. In other words, in most instances, the charging current fed through the battery is independent of the actual charge remaining of the battery. As a result, it is possible for a fully charged battery to still be exposed to a charging current, which can ultimately damage the battery.
For instance, once a battery is fully charged, the charging current has to be dissipated somehow. The result is the generation of heat and gases both of which are bad for the battery. Therefore, it is recognized that to effectively charge a battery it is ideal to detect when the reconstitution of the active battery chemicals is complete and to then terminate the charging process before any damage is done to the battery. One approach is to detect when a predetermined upper voltage limit, often called the termination voltage, has been reached and responsive thereto, switchably disconnect the battery from the charging source, i.e., alternator.
Switchably disconnecting the battery from the alternator has some drawbacks. For example, electronics of the electrical generator will deplete the battery, which may therefore require continuous cycling of the connection of the battery to the alternator. Also, if a fast charge is used when the battery is connected to the alternator, it is possible for more electrical current to be pumped through the battery faster than the chemical processes within the battery can react to the current. On the other hand, if a trickle or slow charge is used, there may not be enough current to fully charge the battery.
The present invention is directed to a battery charging system for charging the battery of an electrical generator and doing so in a manner that extends battery life and maintenance intervals by only applying the amount of charge necessary to maintain a full charge during a charging interval for the battery. Depending upon the charge of the battery, the charge applied to bring the battery to a full charge may be applied in a boost (fast) charge or in a trickle charge.
In one embodiment, the present invention is embodied in executable code that is executed by the general controller of the generator, and in a preferred embodiment, the controller controls charging of the battery but also provides general battery monitoring. In a further preferred embodiment, the circuitry that controls operation of the generator's engine and alternator also controls operation of the battery charging system.
It is therefore an object of the invention to provide a battery charging system for use with an electrical generator that provides dynamic charging of the battery to avoid overcharging of the battery.
It is another object of the invention to provide a system for charging the battery of an electrical generator that selectively applies a fast charge or a trickle charge depending on various real-time characteristics of the battery.
It is a further object of the invention to provide an electrical generator having a battery powered motor starter and a battery charging circuit for charging the battery during operation of the electrical generator, and that charges the battery based on various operational characteristics of the battery, such as voltage level of the battery and battery temperature.
It is yet another object of the present invention to provide a controller for a battery charging circuit of an electrical generator and to power the controller from electrical power generated during operation of the electrical generator.
Other objects, features, and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.